1. Field of the Invention
The present invention relates to an engine cooling system, and more particularly to a cooling system for a multi-cylinder V-type transverse water-cooled engine.
2. Description of the Prior Art
U.S. patent application Ser. No. 439,917 filed Nov. 21, 1989 relates to a cooling system for the above type engine. Such an engine cooling system still has the following problems.
First, the following problem remains concerning a cooling water filling position.
In a cooling system for a water-cooled engine, it is generally necessary to locate a cooling water filler at the highest position of an overall cooling water circulation path. Conventionally, as an upper end of a radiator is present at the highest position of the overall cooling water circulation path, the cooling water filler is located at the upper end of the radiator.
In recent years, it has been demanded to reduce the height of an engine hood of a vehicle. In such a vehicle having a low engine hood, the height of the engine hood is lowest especially in the vicinity of a front end portion of the vehicle. Accordingly, it is necessary to reduce the height of the radiator which is normally located at the front end portion of the vehicle. However, if the upper end of the radiator is present at the highest position of the overall cooling water circulation path, the height of the engine hood of the vehicle cannot be sufficiently reduced. The height of the radiator can be reduced so as not to locate the upper end of the radiator at the highest position of the overall cooling water circulation path. In such case, the cooling water filler cannot be located at the upper end of the radiator.
In this circumstance, there has been proposed an engine cooling system wherein the cooling water filler is located on a cooling water passage communicating the radiator with a water jacket of the engine (see Japanese Patent Laid-open Publication No. 58-210314, for example). In such case, that portion of the cooling water passage where the cooling water filler is located should be located at the highest position of the overall cooling water circulation path. In such a cooling system, since it is not necessary to locate the upper end of the radiator at the highest position of the overall cooling water circulation path, the height of the radiator can be sufficiently reduced. Accordingly, the height of the engine hood of the vehicle can be effectively reduced.
Meanwhile, in a water-cooled multi-cylinder engine having a plurality of cylinder banks, such as a V-type engine, a water jacket is normally formed in each bank. A plurality of cooling water outlet passages for discharging cooling water in the water jackets in the banks are converged at a joining portion which is continued to a common cooling water outlet passage. The common cooling water outlet passage is connected to the radiator (see Japanese Patent Laid-open Publication No. 62-91615). In such an engine cooling system, the diameter of each cooling water outlet passage connected to each bank is smaller than that of a single cooling water outlet passage in a normal in-line engine (having a single bank) having multiple cylinders arranged rectilinearly. In a V-type engine, the amount of the cooling water to be discharged from the water jacket in each bank is about 1/2 of the amount of the cooling water to be discharged from all the water jackets. Therefore, the cross sectional area of each cooling water outlet passage from each bank in the V-type engine is about 1/2 of the cross sectional area of the cooling water outlet passage in the in-line engine.
In such a V-type engine, it is normal to locate the cooling water filler at either the upper end of the radiator or on the common cooling water outlet passage so as to reduce the height of the engine hood. In any case, when cooling water is filled from the cooling water filler into the cooling system after draining the cooling system, the cooling water filled from the cooling water filler is divided from the common cooling water outlet passage to the cooling water outlet passages leading to the respective water jackets in the banks. However, since the cross sectional area of each cooling water outlet passage leading to each water jacket is relatively small as mentioned above, the cooling water flowing into the water jackets interferes with inside air that must be expelled from the water jackets to the cooling water outlet passages. As a result, the inside air is not smoothly expelled and a long time is required for filling the cooling water into the water jackets.
To cope with this problem, it has been considered to enlarge the diameter of each cooling water outlet passage for each bank. However, this causes other problems in relation to cost and space around the engine. Alternatively, it has been considered to provide an air vent through the water jacket in each bank. However, this causes an increase in number of parts, resulting in problems in relation to mountability and cost.
Second, the following problem remains concerning workability, serviceability, sealability and durability of a mounting structure of the cooling water circulation system.
Generally, a cooling system for a water-cooled engine includes a water pump for supplying cooling water to the engine, a cooling water outlet passage for guiding the cooling water from the engine to the radiator, a water return passage for returning the cooling water from the radiator to the engine, a thermostat case connected to a downstream end of the water return passage, a suction passage for communicating a suction side of the water pump with the thermostat case, and a bypass passage for communicating the cooling water outlet passage with the thermostat case.
Particularly in a V-type engine, in order to make the cooling system compact, the water pump is located at a front end of the engine, and the thermostat case is located at a rear end of the engine. Furthermore, the suction passage for connecting the water pump with the thermostat case is located in a V-shaped space defined between two banks, which space is a dead space in the prior art (see Japanese Patent Laid-open Publication No. 62-91615, for example).
In such a cooling system wherein the suction passage is located in the V-shaped space, if the suction passage is fixedly connected at opposite ends thereof to the water pump and the thermostat case, both of which are fixed to the engine, and the engine and the suction passage are formed for example of aluminum alloy and steel material, respectively, strong internal stresses will be generated in the engine or the suction passage in the longitudinal direction thereof when temperature changes occur due to a difference in coefficients of thermal expansion of the materials of the engine and the suction passage. This causes a reduction in durability and sealability of the engine and the cooling system. Such problem also can occur because of errors in dimensions of the suction passage.
In the above conventional cooling system described in Japanese Patent Laid-open Publication No. 62-91615, for example, the opposite ends of the suction passage are displaceably connected through O-rings to the water pump and the thermostat case, so as to prevent the generation of internal stresses due to temperature changes or dimensional errors.
However, as the O-rings are used for the connection of the suction passage in the above conventional cooling system, the number of parts is increased to cause more complexity of mountability and serviceability. Furthermore, the O-rings are hard to position.
Third, the following problem remains concerning cooling performance of the radiator and noise to be generated from a cooling fan.
Generally in a vehicle provided with a water-cooled transverse engine, the radiator is located in the vicinity of a front end of the vehicle in such a manner that a wind receiving surface of the radiator is substantially perpendicular to a longitudinal direction of the vehicle. On the other hand, the engine is located behind the radiator so as to extend in a transverse direction of the vehicle. Further, a motor-driven cooling fan is located just behind the radiator, so as to facilitate the cooling performance of the radiator.
Meanwhile, it has been demanded in recent years to reduce the height of the radiator in relation to the fact that a vehicle with a low engine hood is preferred. To meet this demand, it has been proposed that a vehicle having a transverse engine be provided with a cross flow type radiator having a pair of cooling water tanks located at opposite ends of a radiator body portion, in the transverse direction of the vehicle (see Japanese Patent Laid-open Publication No. 62-91615, for example). In the prior art, such cooling water tanks are located at an upper end and a lower end of the radiator body portion.
However, in such vehicle having the water-cooled transverse engine, the projected area of the engine in the air flowing direction (i.e., the longitudinal direction of the vehicle) is very large. Accordingly, the blowing ability or performance of the cooling fan is hindered by the engine, with the result that the cooling performance of the radiator is reduced.
Further, a cooling water passage for circulating the cooling water between the engine and the radiator is located behind the cooling fan. As a result, the blowing ability of the cooling fan is further hindered by the cooling water passage, thereby further reducing the cooling performance of the radiator. Furthermore, as the air fed from the cooling fan flows around the cooling water passage at a high velocity, a so-called wind noise is generated to cause a large noise of the cooling fan.